Sigma Corporation of America to Release Two MTF Charts for Measurement of Lenses

Company releases the data of Geometric and Diffraction MTF charts for Global Vision Lenses

RONKONKOMA, N.Y., — February 3, 2014 – Sigma Corporation of America, a leading researcher, developer, manufacturer and service provider of some of the world’s most impressive lines of lenses, cameras and flashes, today announced that the company will now release a Geometrical MTF (Modulation Transfer Function) chart in addition to a Diffraction MTF chart when measuring the performance of all new Global Vision lenses.

MTF charts are important because they help photographers better understand the optical quality of lenses. Sigma has traditionally released Diffraction MTF data because it takes the diffraction quality of light into consideration, which can dramatically affect the data outcome. Diffracted light exists at every aperture, giving photographers a more accurate measurement of how the lens will perform in real life. Although Geometric MTF data is easier to measure and calculate since it does not consider the diffraction quality of light, it tends to show higher values in the graph and less defined results.

“As a family-owned organization, we hold ourselves and the products we design to a very high standard,” said Mark Amir-Hamzeh, president of Sigma Corporation of America. “Our customer’s expect high quality products and by sharing both MTF charts for all our new lenses, we are able to help guide them in making the most informed purchase decisions based on how our lenses will perform in actual photography situations.”

As a leader in technology and innovation, Sigma Corporation is committed to showing the true value and quality standards of all Sigma Global Vision lenses. Every lens is tested with Sigma’s proprietary modulation transfer function (MTF) “A1” measuring system before being shipped from the factory in Japan. By making both MTF charts available, Sigma is providing its customers with accurate measurements of its lenses and giving photographers a chance to see the full potential of Sigma’s lenses.

I wouldn't think so – people would start comparing, trying to get the best one they could, and returning lens after lens to do so. Rather, they test each lens as part of their QC process, and as long as it meets their minimum standard the lens is packed and shipped to be sold.

I wouldn't think so – people would start comparing, trying to get the best one they could, and returning lens after lens to do so. Rather, they test each lens as part of their QC process, and as long as it meets their minimum standard the lens is packed and shipped to be sold.

I honestly thought of that too. Thing is, then what is the announcement about? What additional MTF are they going to publish?

Thing is, then what is the announcement about? What additional MTF are they going to publish?

They're publishing a geometric MTF in addition to the diffraction MTF that they already publish. The diffraction MTF takes diffraction of light into account, in addition to aberrations. Diffraction limits the maximum resolution of lenses as the aperture gets smaller. A geometric MTF ignores the effect of diffraction - in practice that means the f/8 lines will move up higher on the chart (higher is better).

Please reconsider the nonsense that you wrote. Sigma is the manufacturer, not the retailer to end users. You don't buy from them, how can they give you money *back* and *worldwide*?

Ditto.

Consider what the retailer must do with the returned lenses. Nothing. It's a dead loss.

The only possible solution would be if Sigma supports their retailers and takes back the lenses, refurbishes them, repackages them, gives the retailer credit for the lens, etc. and whatever. This means Sigma takes all the responsibility without placing a strain on the retailer.

Worldwide ... us here in Africa do not have the luxury of "mail-in rebates" from manufacturers, because Canon for one does not support their consumers equally worldwide.

Logged

Happily ignoring the laws of physics and the rules of photography to create better pictures.

By making both MTF charts available, Sigma is providing its customers with accurate measurements of its lenses and giving photographers a chance to see the full potential of Sigma’s lenses.

I don't care about MTF charts. If Sigma wants me to consider their lenses, then offer a no-questions-asked 30-day money-back guarantee - world-wide, of course.

In fact, it would be a demonstration of respect for the consumer if Sigma had authorized service centers in all countries with over 100 million inhabitants. In Brazil we have 200 million inhabitants and no Sigma authorized service. Currently, even the small enterprise Tokina has authorized service center in Brazil, and Sigma has not. Could give even more credibility to Sigma offers a 5 year warranty on all countries, as does the Tamron in the USA. That way I would feel safe in buying Sigma products again.

Thing is, then what is the announcement about? What additional MTF are they going to publish?

They're publishing a geometric MTF in addition to the diffraction MTF that they already publish. The diffraction MTF takes diffraction of light into account, in addition to aberrations. Diffraction limits the maximum resolution of lenses as the aperture gets smaller. A geometric MTF ignores the effect of diffraction - in practice that means the f/8 lines will move up higher on the chart (higher is better).

So which type does Canon publish for their lenses?

Canon's are diffraction MTFs (I'm pretty sure everyone's are, actually, although that may not have been the case before computer-based lens design).

Like most manufacturers, Canon's are theoretical MTFs generated from mathematical modeling of the optical forumla of the lens. Although Sigma apparently empirically measures the MTF of all their production lenses as part of QC, I presume their published MTF curves for each lens are theoretical. Note that Sigma is wrong when they state, "Although Geometric MTF data is easier to measure and calculate…" – easier to calculate, yes, but you can't actually measure a geometical MTF, becuase real light passed through a real lens to measure MTF is subject to diffraction (they're also gramatically incorrect, data are plural ). With modern (even not that modern) computers, a diffraction MTF is easy to calculate once the optical design is known.

So after all is said and done, this geometric MTF is a completely useless graph, because it shows numbers that can't be achieved if all laws of optics are considered. The biggest benefit from this graph seems to be a cheap marketing ploy aimed at folks who don't know better: "Look at the F/22 numbers, the Sigma lens is so much sharper compared to all others!"

I'm amazed that Sigma has the gall to make a public press announcement about this ...

So after all is said and done, this geometric MTF is a completely useless graph, because it shows numbers that can't be achieved if all laws of optics are considered.

Well, with a lens wide open the effects of diffraction are minimal so performance approaches the geometric model. But then, the algorithms that generate the diffraction MTFs take that into account, and for a wide open lens the two plots would be almost identical. So...you're right, still useless.